Interactive projector and interactive projection system

ABSTRACT

An interactive projector includes a projection section, a first detection light irradiation section and a second detection light irradiation section, an imaging section, and a position detection section adapted to detect a position of the pointing element based on an image, which is taken by the imaging section and includes the pointing element. The first and second detection light irradiation sections are disposed so that at least one of the following (i) and (ii) becomes higher than a threshold value: (i) a first contrast between the pointing element in a first image in a case in which the detection light is emitted only from the first detection light irradiation section and the projected screen, and (ii) a second contrast between the pointing element in a second image in a case in which the detection light is emitted only from the second detection light irradiation section and the projected screen.

The entire disclosure of Japanese Patent Application No. 2015-065667,filed Mar. 27, 2015 is expressly incorporated by reference herein.

BACKGROUND

1. Technical Field

The present invention relates to an interactive projector and a systemthereof each capable of receiving an instruction of the user to aprojection screen with a pointing element.

2. Related Art

JP-A-2012-150636 discloses a projection display device (projector)capable of projecting a projected screen on a screen, and at the sametime taking an image, which includes an object such as a finger, with acamera to detect the position of the object using the taken image. Theobject such as a finger is used as a pointing element for making aninstruction to the projected screen. In other words, when the tip of theobject is in contact with the screen, the projector recognizes that apredetermined instruction such as drawing is input to the projectedscreen, and then redraws the projected screen in accordance with theinstruction. Therefore, it is possible for the user to input a varietyof instructions using the projected screen as a user interface. Theprojector of the type capable of using the projected screen on thescreen as an inputting user interface as described above is referred toas an “interactive projector.” Further, the object used for making aninstruction to the projected screen is referred to as a “pointingelement.”

In the interactive projector, in order to detect the position of thepointing element, the pointing element is irradiated with detectionlight such as an infrared ray, and the detection light reflected by thepointing element is imaged by the camera. When detecting the position ofthe pointing element from the image thus taken, where in the image thepointing element is located is determined using a difference in contrastbetween the pointing element and the projected screen. Therefore, in theimage taken by the camera, it is desired that the difference in contrastbetween the pointing element and the projected screen is sufficientlyhigh.

However, the inventors of the invention have found out the fact that itis not necessarily easy to sufficiently enlarge the contrast between thepointing element and the projected screen, and in some cases, thecontrast cannot sufficiently be obtained depending on the way ofapplying the detection light.

SUMMARY

An advantage of some aspects of the invention is to solve at least apart of the problems described above, and the invention can beimplemented as the following aspects or application examples.

(1) An aspect of the invention provides an interactive projector capableof receiving an instruction of a user to a projected screen with apointing element. The interactive projector includes a projectionsection adapted to project the projected screen on a screen surface, afirst detection light irradiation section and a second detection lightirradiation section each adapted to emit detection light used fordetection of the pointing element toward an area of the projectedscreen, an imaging section adapted to receive light in a wavelengthrange including a wavelength of the detection light to take an image ofthe area of the projected screen, and a position detection sectionadapted to detect a position of the pointing element with respect to theprojected screen based on an image, which is taken by the imagingsection and includes the pointing element. In a state in which a tip ofthe pointing element is in contact with an arbitrary position in thearea of the projected screen, the first detection light irradiationsection and the second detection light irradiation section are disposedso that at least one of the following (i) and (ii) becomes higher than athreshold value set in advance for distinguishing the pointing elementfrom the projected screen: (i) a first contrast between the pointingelement in a first image taken by the imaging section in a case in whichthe detection light is emitted only from the first detection lightirradiation section and an area of the projected screen, and (ii) asecond contrast between the pointing element in a second image taken bythe imaging section in a case in which the detection light is emittedonly from the second detection light irradiation section and the area ofthe projected screen.

According to this interactive projector, since at least one of the firstcontrast and the second contrast becomes higher than the threshold valueset in advance at any position in the projected screen, the position ofthe pointing element with respect to the projected screen can bedetermined at any position in the projected screen.

(2) In the interactive projector described above, in a state in whichthe tip of the pointing element is in contact with at least a part ofthe area in the projected screen, the first detection light irradiationsection and the second detection light irradiation section may bedisposed so that if the first contrast is positive, then the secondcontrast is negative, and if the first contrast is negative, then thesecond contrast is positive, and the first detection light irradiationsection and the second detection light irradiation section may emit thedetection light toward the projected screen in a time-multiplexedmanner.

According to this configuration, even if there exists an area where ifthe contrast obtained by the first detection light irradiation sectionis positive, then the contrast obtained by the second detection lightirradiation section is negative, and if the contrast obtained by thefirst detection light irradiation section is negative, then the contrastobtained by the second detection light irradiation section is positive,since the first detection light irradiation section and the seconddetection light irradiation section performs the irradiation in atime-multiplexed manner, the position of the pointing element withrespect to the projected screen can be determined.

(3) In the interactive projector described above, the first detectionlight irradiation section and the second detection light irradiationsection may be disposed on opposite sides to each other across a virtualplane including a normal line of the projected screen at a center of theprojected screen.

According to this configuration, although the direction of the shadow ofthe pointing element formed by the detection light from the firstdetection light irradiation section and the direction of the shadow ofthe pointing element formed by the detection light from the seconddetection light irradiation section become opposite to each other in thevicinity of the center of the projected screen, since both of the firstcontrast and the second contrast become higher than the threshold valueset in advance, the position of the pointing element with respect to theprojected screen can be determined.

(4) The interactive projector described above may further include athird detection light irradiation section disposed at a position closerto the virtual plane than the first detection light irradiation sectionand the second detection light irradiation section, and adapted toirradiate the area of the projected screen with the detection light.

According to this configuration, it is possible to further raise thecontrast between the pointing element and the projected screen.

The invention can be implemented in a variety of configurations such as,for example, a system including either one or both of the screen and thelight-emitting pointing element and the interactive projector, a controlmethod or a control device of the interactive projector, a computerprogram for realizing the method or the functions of the device, or anon-transitory storage medium recoding the computer program.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanyingdrawings, wherein like numbers reference like elements.

FIG. 1 is a perspective view of an interactive projection system.

FIGS. 2A and 2B are a side view and a front view, respectively, of theinteractive projection system.

FIG. 3 is a block diagram showing an internal configuration of aprojector and a light-emitting pointing element.

FIGS. 4A and 4B are explanatory diagrams showing an appearance of anoperation using the light-emitting pointing element and anon-light-emitting pointing element.

FIGS. 5A and 5B are explanatory diagrams each showing incident angles ofthe detection light to a projected screen and the non-light-emittingpointing element.

FIGS. 6A and 6B are explanatory diagrams showing the contrast obtainedby two detection light irradiation sections in a comparative manner.

FIGS. 7A and 7B are a side view and a front view, respectively, of aninteractive projection system according to a second embodiment.

FIGS. 8A and 8B are a side view and a front view, respectively, of aninteractive projection system according to a third embodiment.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

A. General Description of System

FIG. 1 is a perspective view of an interactive projection system 900according to an embodiment of the invention. The system 900 has aninteractive projector 100, a screen plate 920, and a light-emittingpointing element 70. The front surface of the screen plate 920 is usedas a projection screen surface SS. The projector 100 is fixed in frontof and above the screen plate 920 with a support member 910. It shouldbe noted that although the projection screen surface SS is verticallydisposed in FIG. 1, it is also possible to use the system 900 with theprojection screen surface SS disposed horizontally.

The projector 100 projects a projected screen PS on the projectionscreen surface SS. The projected screen PS normally includes an imagedrawn in the projector 100. In the case in which the image drawn in theprojector 100 does not exist, the light is emitted on the projectedscreen PS from the projector 100 to display a white image. In thepresent embodiment, the “projection screen surface SS” (or a “screensurface SS”) denotes a surface of a member on which the image isprojected. Further, the “projected screen PS” denotes an area of animage projected on the projection screen surface SS by the projector100. Normally, the projected screen PS is projected on a part of theprojection screen surface SS.

The light-emitting pointing element 70 is a pen-shaped pointing elementhaving a tip portion 71 capable of emitting light, a sleeve section 72held by the user, and a button switch 73 provided to the sleeve section72. The configuration and the function of the light-emitting pointingelement 70 will be described later. In the system 900, one or morenon-light-emitting pointing elements 80 (e.g., non-light-emitting pensor fingers) can be used together with one or more light-emittingpointing elements 70.

FIG. 2A is a side view of the interactive projection system 900, andFIG. 2B is a front view thereof. In the present specification, adirection along a horizontal direction of the screen surface SS isdefined as an X direction, a direction along a vertical direction of thescreen surface SS is defined as a Y direction, and a direction along anormal line of the screen surface SS is defined as a Z direction. Itshould be noted that the X direction is also referred to as a“horizontal direction,” the Y direction is also referred to as a“vertical direction,” and the Z direction is also referred to as an“anteroposterior direction” for the sake of convenience. Further, amongdirections along the Y direction (the vertical direction), the directionin which the projected screen PS exists viewed from the projector 100 isreferred to as a “downward direction.” It should be noted that in FIG.2A, the range of the projected screen PS out of the screen plate 920 isprovided with hatching for the sake of convenience of graphicaldescription.

The projector 100 has a projection lens 210 for projecting the projectedscreen PS on the screen surface SS, a first camera 310 and a secondcamera 320 for taking images of the area of the projected screen PS, andtwo detection light irradiation sections 411, 412 for illuminating thepointing element (the light-emitting pointing element 70 and thenon-light-emitting pointing element 80) with the detection light. As thedetection light, near infrared light, for example, is used. The twocameras 310, 320 each have at least a first imaging function forreceiving light in a wavelength region including the wavelength of thedetection light to perform imaging. It is preferable for at least one ofthe two cameras 310, 320 to be further provided with a second imagingfunction for receiving light including visible light to perform imaging,and to be configured so as to be able to switch between these twoimaging functions. For example, it is preferable for each of the twocameras 310, 320 to be provided with a near infrared filter switchingmechanism (not shown) capable of placing a near infrared filter, whichblocks visible light and transmits only the near infrared light, infront of a lens and retracting the near infrared filter from the frontof the lens.

The example shown in FIG. 2B shows the state in which the interactiveprojection system 900 acts in a whiteboard mode. The whiteboard mode isa mode in which the user can arbitrarily draw a picture on the projectedscreen PS using the light-emitting pointing element 70 or thenon-light-emitting pointing element 80. The projected screen PSincluding a toolbox TB is projected on the screen surface SS. Thetoolbox TB includes a cancel button UDB for undoing the process, apointer button PTB for selecting a mouse pointer, a pen button PEB forselecting the pen tool for drawing an image, an eraser button ERB forselecting an eraser tool for erasing the image thus drawn, andforward/backward button FRB for feeding the screen forward or backward.By clicking these buttons using the pointing element, the user canperform processes corresponding to the respective buttons, or can selecttools corresponding to the respective buttons. It should be noted thatit is also possible to arrange that the mouse pointer is selected as adefault tool immediately after starting up the system 900. In theexample shown in FIG. 2B, there is described the appearance in which aline is being drawn in the projected screen PS by the user selecting thepen tool, and then moving the tip portion 71 of the light-emittingpointing element 70 within the projected screen PS in the state ofhaving contact with the screen surface SS. The drawing of the line isperformed by a projection image generation section (described later)inside the projector 100.

It should be noted that the interactive projection system 900 can act inother modes than the whiteboard mode. For example, this system 900 canalso act in a PC interactive mode for displaying an image of the data,which is transferred from a personal computer (not shown) via acommunication line, on the projected screen PS. In the PC interactivemode, an image of the data of, for example, spreadsheet software isdisplayed, and it becomes possible to perform input, generation,correction, and so on of the data using a variety of tools and iconsdisplayed in the image.

FIG. 3 is a block diagram showing the internal configuration of theinteractive projector 100 and the light-emitting pointing element 70.The projector 100 has a control section 700, a projection section 200, aprojection image generation section 500, a position detection section600, an imaging section 300, a detection light irradiation section 410,and a signal light transmission section 430. The detection lightirradiation section 410 includes the first detection light irradiationsection 411 and the second detection light irradiation section 412.

The control section 700 performs the control of each of the sectionsinside the projector 100. Further, the control section 700 determinesthe content of the instruction performed on the projected screen PS bythe pointing element (the light-emitting pointing element 70 or thenon-light-emitting pointing element 80) detected by the positiondetection section 600, and at the same time commands the projectionimage generation section 500 to generate or change the projection imagein accordance with the content of the instruction.

The projection image generation section 500 has a projection imagememory 510 for storing the projection image, and has a function ofgenerating the projection image to be projected on the screen surface SSby the projection section 200. It is preferable for the projection imagegeneration section 500 to further have a function as a keystonedistortion correction section for correcting a keystone distortion ofthe projected screen PS (FIG. 2B).

The projection section 200 has a function of projecting the projectionimage, which has been generated by the projection image generationsection 500, on the screen surface SS. The projection section 200 has alight modulation section 220 and a light source 230 besides theprojection lens 210 explained with reference to FIGS. 2A and 2B. Thelight modulation section 220 modulates the light from the light source230 in accordance with the projection image data provided from theprojection image memory 510 to thereby form projection image light IML.The projection image light IML is typically a color image lightincluding the visible light of three colors of RGB, and is projected onthe screen surface SS by the projection lens 210. It should be notedthat as the light source 230, there can be adopted a variety of types oflight sources such as a light emitting diode or a laser diode besides alight source lamp such as a super-high pressure mercury lamp. Further,as the light modulation section 220, there can be adopted a transmissiveor reflective liquid crystal panel, a digital mirror device, or thelike, and it is also possible to adopt a configuration provided with aplurality of light modulation sections 220 for respective colored lightbeams.

The two detection light irradiation sections 411, 412 irradiatethroughout the screen surface SS and the space in front of the screensurface SS with irradiating detection light IDL for detecting the tipportion of the pointing element (the light-emitting pointing element 70or the non-light-emitting pointing element 80). As the irradiatingdetection light IDL, near infrared light, for example, is used. Thedetection light irradiation sections 411, 412 are put on only in apredetermined period including imaging timing of the cameras 310, 320,and are put off in other periods. Alternatively, it is also possible toarrange that the detection light irradiation sections 411, 412 arealways kept in the lighting state while the system 900 is in action.

The signal light transmission section 430 has a function of transmittinga device signal light ASL to be received by the light-emitting pointingelement 70. The device signal light ASL is the near infrared signal forsynchronization, and is periodically emitted from the signal lighttransmission section 430 of the projector 100 to the light-emittingpointing element 70. A tip light emitting section 77 of thelight-emitting pointing element 70 emits pointing element signal lightPSL (described later) as the near infrared light having a predeterminedlight emission pattern (light emission sequence) in sync with the devicesignal light ASL. Further, when performing the position detection of thepointing element (the light-emitting pointing element 70 or thenon-light-emitting pointing element 80), the cameras 310, 320 of theimaging section 300 perform imaging at predetermined timingssynchronized with the device signal light ASL.

The imaging section 300 has the first camera 310 and the second camera320 explained with reference to FIGS. 2A and 2B. As described above, thetwo cameras 310, 320 each have the function for receiving light in awavelength region including the wavelength of the detection light toperform imaging. In the example shown in FIG. 3, there is described theappearance in which the irradiating detection light IDL emitted by thedetection light irradiation section 411 is reflected by the pointingelement (the light-emitting pointing element 70 or thenon-light-emitting pointing element 80), and then the reflecteddetection light RDL is received by the two cameras 310, 320 to beimaged. The two cameras 310, 320 further receives the pointing elementsignal light PSL, which is the near infrared light emitted from the tiplight emitting section 77 of the light-emitting pointing element 70, toperform imaging. Imaging by the two cameras 310, 320 is performed inboth of a first period, in which the irradiating detection light IDLemitted from the detection light irradiation section 410 is in an ONstate (light-emitting state), and a second period in which theirradiating detection signal IDL is in an OFF state (non-light-emittingstate). It is possible for the position detection section 600 to comparethe images in the respective two types of periods to thereby determinewhich one of the light-emitting pointing element 70 and thenon-light-emitting pointing element 80 each of the pointing elementsincluded in the images corresponds to.

It should be noted that at least one of the two cameras 310, 320preferably has a function of performing imaging using the lightincluding the visible light in addition to a function of performingimaging using the light including the near infrared light. By adoptingthis configuration, it is possible to take images of the projectedscreen PS projected on the screen surface SS with the cameras, and thenmake the projection image generation section 500 perform the keystonedistortion correction using the images. Since the method of the keystonedistortion correction using one or more cameras is well known, theexplanation thereof will be omitted here.

The position detection section 600 has a function of determining thethree-dimensional position of the tip portion of the pointing element(the light-emitting pointing element 70 or the non-light-emittingpointing element 80) making use of triangulation using the images takenby the two cameras 310, 320. On this occasion, the position detectionsection 600 also determines which one of the light-emitting pointingelement 70 and the non-light-emitting pointing element 80 each of thepointing elements in the images corresponds to using the light emissionpattern of the light-emitting pointing element 70.

The light-emitting pointing element 70 is provided with a signal lightreception section 74, a control section 75, a tip switch 76, and a tiplight emitting section 77 besides the button switch 73. The signal lightreception section 74 has a function of receiving a device signal lightASL emitted from the signal light transmission section 430 of theprojector 100. The tip switch 76 is a switch to be set to an ON statewhen the tip portion 71 of the light-emitting pointing element 70 ispushed, and set to an OFF state when the tip portion 71 is released. Thetip switch 76 is normally in the OFF state, and is set to the ON statedue to contact pressure if the tip portion 71 of the light-emittingpointing element 70 is in contact with the screen surface SS. When thetip switch 76 is in the OFF state, the control section 75 makes the tiplight emitting section 77 emit light with a specific first lightemission pattern representing that the tip switch 76 is in the OFF stateto thereby emit the pointing element signal light PSL having the firstemission pattern. In contrast, when the tip switch 76 becomes in the ONstate, the control section 75 makes the tip light emitting section 77emit light with a specific second light emission pattern representingthat the tip switch 76 is in the ON state to thereby emit the pointingelement signal light PSL having the second emission pattern. Since thefirst emission pattern and the second emission pattern are differentfrom each other, it is possible for the position detection section 600to analyze the images taken by the two cameras 310, 320 to therebydetermine whether the tip switch 76 is in the ON state or in the OFFstate.

As described above, in the present embodiment, the contact determinationon whether or not the tip section 71 of the light-emitting pointingelement 70 is in contact with the screen surface SS is performed inaccordance with ON/OFF of the tip switch 76. Incidentally, since thethree-dimensional position of the tip section 71 of the light-emittingpointing element 70 can be obtained by the triangulation using theimages taken by the two cameras 310, 320, it is also possible to performthe contact determination of the tip portion 71 of the light-emittingpointing element 70 using the three-dimensional position. It should benoted that the detection accuracy of the Z coordinate (the coordinate inthe normal direction of the screen surface SS) due to the triangulationis not necessarily high in some cases. Therefore, it is preferable toarrange that the contact determination is performed in accordance withON/OFF of the tip switch 76 in the point that the contact determinationcan more accurately be performed.

The button switch 73 of the light-emitting pointing element 70 has thesame function as that of the tip switch 76. Therefore, the controlsection 75 makes the tip light emitting section 77 emit light with thesecond light emission pattern described above in the state in which theuser holds down the button switch 73, and makes the tip light emittingsection 77 emit light with the first light emission pattern describedabove in the state in which the button switch 73 is not held down. Inother words, the control section 75 makes the tip light emitting section77 emit light with the second light emission pattern described above inthe state in which at least one of the tip switch 76 and the buttonswitch 73 is in the ON state, and makes the tip light emitting section77 emit light with the first light emission pattern described above inthe state in which both of the tip switch 76 and the button switch 73are in the OFF state.

It should be noted that it is also possible to arrange that a differentfunction from that of the tip switch 76 is assigned to the button switch73. For example, in the case in which the same function as that of aright-click button of the mouse is assigned to button switch 73, whenthe user holds down the button switch 73, an instruction of the rightclick is transmitted to the control section 700 of the projector 100,and the process corresponding to the instruction is executed. In thecase in which the different function from that of the tip switch 76 isassigned to the button switch 73 as described above, the tip lightemitting section 77 emits light with four light emission patternsdifferent from each other in accordance with the ON/OFF state of the tipswitch 76 and the ON/OFF state of the button switch 73. In this case, itis possible for the light-emitting pointing element 70 to maketransmission to the projector 100 while distinguishing the fourcombinations of the ON/OFF states of the tip switch 76 and the buttonswitch 73.

FIGS. 4A and 4B are explanatory diagrams showing an appearance of anoperation using the light-emitting pointing element 70 and thenon-light-emitting pointing element 80. In this example, both of the tipportion 71 of the light-emitting pointing element 70 and the tip portion81 of the non-light-emitting pointing element 80 are separated from thescreen surface SS. The X-Y coordinate (X₇₁, Y₇₁) of the tip portion 71of the light-emitting pointing element 70 is located on the eraserbutton ERB of the toolbox TB. Further, here, the mouse pointer PT isselected as a tool for representing the function of the tip portion 71of the light-emitting pointing element 70, and the mouse pointer PT isdrawn in the projected screen PS so that the tip OP₇₁ of the mousepointer PT exists on the eraser button ERB. As described above, thethree-dimensional position of the tip portion 71 of the light-emittingpointing element 70 is determined by the triangulation using the imagestaken by the two cameras 310, 320. Therefore, on the projected screenPS, the mouse pointer PT is drawn so that the operation point OP₇₁located at the tip of the mouse pointer PT is disposed at the positionof the X-Y coordinate (X₇₁, Y₇₁) out of the three-dimensional coordinate(X₇₁, Y₇₁, Z₇₁) of the tip portion 71 determined by the triangulation.In other words, the tip OP₇₁ of the mouse pointer PT is disposed at theX-Y coordinate (X₇₁, Y₇₁) out of the three-dimensional coordinate (X₇₁,Y₇₁, Z₇₁) of the tip portion 71 of the light-emitting pointing element70, and the instruction of the user is performed at this position. Forexample, it is possible for the user to select the eraser tool byholding down the button switch 73 of the light-emitting pointing element70 in this state. As described above, in the present embodiment, even inthe case in which the light-emitting pointing element 70 is in the stateof being separated from the screen surface SS, it is possible to providethe instruction, which corresponds to the content of the projectedscreen PS in the operation point OP₇₁ located at the X-Y coordinate(X₇₁, Y₇₁) of the tip portion 71, to the projector 100 by holding downthe button switch 73.

In FIG. 4B, the pen tool PE is further selected as the tool representingthe function of the tip portion 81 of the non-light-emitting pointingelement 80, and the pen tool PE is drawn on the projected screen PS. Asdescribed above, the three-dimensional position of the tip portion 81 ofthe non-light-emitting pointing element 80 is also determined by thetriangulation using the images taken by the two cameras 310, 320.Therefore, on the projected screen PS, the pen tool PE is drawn so thatthe operation point OP₈₁ located at the tip of the pen tool PE isdisposed at the position of the X-Y coordinate (X₈₁, Y₈₁) out of thethree-dimensional coordinate (X₈₁, Y₈₁, Z₈₁) of the tip portion 81determined by the triangulation. It should be noted that when the userprovides the instruction to the projector 100 using thenon-light-emitting pointing element 80, the instruction (e.g., drawingand selection of the tool) is performed in the state of making the tipportion 81 of the non-light-emitting pointing element 80 have contactwith the projected screen PS.

In the example shown in FIGS. 4A and 4B, even in the case in which thetip portions of the pointing elements (the light-emitting pointingelement 70 and the non-light-emitting pointing element 80) are separatedfrom the projected screen PS, the tool (the mouse pointer PT or the pentool PE) selected by each of the pointing elements is drawn on theprojected screen PS to thereby be displayed. Therefore, there is anadvantage that it is easy to understand what tools are selected by thepointing elements even in the case in which the user does not make thetip portions of the pointing elements have contact with the projectedscreen PS, and thus, the operation is easy. Further, since the tool isdrawn so that the operation point OP of the tool is disposed at theposition of the X-Y coordinate out of the three-dimensional coordinateof the tip portion of the pointing element, there is an advantage thatthe user can appropriately recognize the position of the tool in use.

It should be noted that the interactive projection system 900 can alsobe configured so that two or more light-emitting pointing elements 70can simultaneously be used. In this case, the light emission patterns ofthe pointing element signal light PSL described above are preferablyunique light emission patterns with which the two or more light-emittingpointing elements 70 can be identified. More specifically, in the casein which the N (N is an integer equal to or greater than 2)light-emitting pointing elements 70 can be used at the same time, thelight emission patterns of the pointing element signal light PSL arepreferably the patterns with which the N light-emitting pointingelements 70 can be distinguished from each other. It should be notedthat in the case in which a plurality of unit light emission periods isincluded in a set of light emission patterns, two values, namelyemission and non-emission, can be expressed in each of the unit lightemission periods. Here, each of the unit light emission periodscorresponds to the period for expressing 1-bit information, namely theON/OFF state of the tip light emitting section 77 of the light-emittingpointing element 70. In the case in which the set of light emissionpatterns are each formed of M (M is an integer equal to or greater than2) unit light emission periods, 2^(M) states can be distinguished by theset of light emission patterns. Therefore, it is preferable for thenumber M of the unit light emission periods constituting each of the setof the light emission patterns to be set so as to fulfill the followingformula.N×Q≤2^(M)  (1)

Here, Q is a number of the states distinguished by the switches 73, 76of the light-emitting pointing element 70, and in the example of thepresent embodiment, Q=2 or Q=4 is set. For example, in the case of Q=4,it is preferable that if N=2, M is set to an integer equal to or greaterthan 3, and if N=3 through 4, M is set to an integer equal to or greaterthan 4. In this case, when the position detection section 600 (or thecontrol section 700) identifies the N light-emitting pointing elements70, and the states of the switches 73, 76 of each of the light-emittingpointing elements 70, the identification is performed using the M imagestaken in each of the cameras 310, 320 in the M unit light emissionperiods of the set of light emission patterns. It should be noted thatthe M-bit light emission patterns are the patterns of setting thepointing element signal light PSL to the ON state or the OFF state inthe state of keeping the irradiating detection light IDL in the OFFstate, and therefore the non-light-emitting pointing element 80 does notshow in the images taken by the cameras 310, 320. Therefore, it ispreferable to further add 1-bit unit light emission period with theirradiating detection light IDL set to the ON state for taking images tobe used for detecting the position of the non-light-emitting pointingelement 80. It should be noted that in the unit light emission periodfor the position detection, the pointing element signal light PSL can bein either of the ON state and the OFF state. The images obtained in theunit light emission period for the position detection can also be usedfor the position detection of the light-emitting pointing elements 70.

The five specific examples of the signal light described in FIG. 3 aresummed up as follows.

(1) Projection Image Light IML: the image light (visible light)projected on the screen surface SS by the projection lens 210 in orderto project the projected screen PS on the screen surface SS.

(2) Irradiating Detection Light IDL: the near infrared light with whichthe detection light irradiation section 410 (411, 412) irradiatesthroughout the screen surface SS and the space in front of the screensurface SS for detecting the tip portions of the pointing elements (thelight-emitting pointing element 70 and the non-light-emitting pointingelement 80).

(3) Reflected Detection Light RDL: the near infrared light reflected bythe pointing elements (the light-emitting pointing element 70 and thenon-light-emitting pointing element 80), and then received by the twocameras 310, 320 out of the near infrared light emitted as theirradiating detection light IDL.

(4) Device Signal Light ASL: the near infrared light periodicallyemitted from the signal light transmission section 430 of the projector100 in order to synchronize the projector 100 and the light-emittingpointing element 70 with each other.

(5) Pointing Element Signal Light PSL: the near infrared light emittedfrom the tip light emitting section 77 of the light-emitting pointingelement 70 at the timing synchronized with the device signal light ASL.The light emission pattern of the pointing element signal light PSL ischanged in accordance with the ON/OFF states of the switches 73, 76 ofthe light-emitting pointing element 70. Further, the unique lightemission patterns for identifying the plurality of light-emittingpointing elements 70.

In the present embodiment, the position detection of the tip portions ofthe light-emitting pointing element 70 and the non-light-emittingpointing element 80, and the determination of the contents instructed bythe light-emitting pointing element 70 and the non-light-emittingpointing element 80 are performed as follows.

General Description of Position Detection Method of Light-EmittingPointing Element 70 and Determination Method of Instruction Contents

The three-dimensional position (X₇₁, Y₇₁, Z₇₁) of the tip portion 71 ofthe light-emitting pointing element 70 is determined by the positiondetection section 600 due to the triangulation using the images taken bythe two cameras 310, 320. On this occasion, whether or not the pointingelement is the light-emitting pointing element 70 can be recognized bydetermining whether or not the light emission pattern of the tip lightemitting section 77 appears in the images taken at a predeterminedplurality of timings. Further, whether or not the tip portion 71 of thelight-emitting pointing element 70 is in contact with the screen surfaceSS (i.e., whether or not the tip switch 76 is in the ON state) can alsobe determined using the light emission pattern of the tip light emittingsection 77 in the images taken at the plurality of timings describedabove. The position detection section 600 can further determine thecontent of the instruction in accordance with the ON/OFF states of theswitches 73, 76, and the content of the projection screen surface SS atthe X-Y coordinate (X₇₁, Y₇₁) of the tip portion 71 of thelight-emitting pointing element 70. For example, as shown in FIG. 4B asan example, in the case in which the tip switch 76 becomes in the ONstate in the state in which the position of the X-Y coordinate (X₇₁,Y₇₁) of the tip portion 71 is located on either of the buttons in thetoolbox TB, the tool of that button is selected. Further, as shown inFIG. 2B as an example, if the X-Y coordinate (X₇₁, Y₇₁) of the tipportion 71 is located at a position outside the toolbox TB in theprojected screen PS, the process (e.g., drawing) using the tool thusselected. The control section 700 makes the projection image generationsection 500 draw a pointer or a mark selected in advance so that thepointer or the mark is disposed at the position (X₇₁, Y₇₁) in theprojected screen PS using the X-Y coordinate (X₇₁, Y₇₁) of the tipportion 71 of the light-emitting pointing element 70. Further, thecontrol section 700 performs the process corresponding to the contentinstructed by the light-emitting pointing element 70, and then makes theprojection image generation section 500 draw the image including theprocessing result.

General Description of Position Detection Method of Non-Light-EmittingPointing Element 80 and Determination Method of Instruction Contents

The three-dimensional position (X₈₁, Y₈₁, Z₈₁) of the tip portion 81 ofthe non-light-emitting pointing element 80 is also determined due to thetriangulation using the images taken by the two cameras 310, 320. Onthis occasion, whether or not the pointing element is thenon-light-emitting pointing element 80 can be recognized by determiningwhether or not the light emission pattern of the light-emitting pointingelement 70 appears in the images taken at a predetermined plurality oftimings. It should be noted that the positions of the tip portions 81 ofthe non-light-emitting pointing element 80 in the two images taken bythe two cameras 310, 320 can be determined using a well known technologysuch as template matching or feature extraction. For example, in thecase of recognizing the tip portion 81 of the non-light-emittingpointing element 80 as a finger using the template matching, the tipportion 81 of the finger can be recognized by preparing a plurality oftemplates related to the finger in advance, and then searching theimages taken by the two cameras 310, 320 for the part matching thesetemplates. Further, whether or not the tip portion 81 of thenon-light-emitting pointing element 80 is in contact with the screensurface SS can be determined in accordance with whether or not thedifference between the Z coordinate value of the tip portion 81determined by the triangulation and the Z coordinate value of the screensurface SS is equal to or smaller than a minute allowable tolerance,namely whether or not the tip portion 81 is sufficiently close to thescreen surface SS. As the allowable tolerance, it is preferable to use asmall value in a range of, for example, about 2 mm through 6 mm.Further, in the case in which the position detection section 600determines that the tip portion 81 of the non-light-emitting pointingelement 80 is in contact with the screen surface SS, the positiondetection section 600 determines the instruction content in accordancewith the content of the projection screen surface SS at the contactposition. The control section 700 makes the projection image generationsection 500 draw a pointer or a mark selected in advance so that thepointer or the mark is disposed at the position (X₈₁, Y₈₁) in theprojected screen PS using the X-Y coordinate (X₈₁, Y₈₁) of the tip ofthe non-light-emitting pointing element 80 detected by the positiondetection section 600. Further, the control section 700 performs theprocess corresponding to the content instructed by thenon-light-emitting pointing element 80, and then makes the projectionimage generation section 500 draw the image including the processingresult.

B. Detection Light Irradiation Section in First Embodiment

FIGS. 5A and 5B are explanatory diagrams showing incident angles θ_(ss),θ_(fg) of the detection light IDL emitted from the detection lightirradiation section 411 with respect to the projected screen PS and thenon-light-emitting pointing element 80, respectively. FIG. 5A shows thecase in which the non-light-emitting pointing element 80 is located in arelatively lower area of the projected screen PS, and FIG. 5B shows thecase in which the non-light-emitting pointing element 80 is located in arelatively upper area of the projected screen PS. In these drawings,there are shown the incident angles θ_(ss), θ_(fg) of the detectionlight IDL at the position of the tip of the non-light-emitting pointingelement 80. The incident angles θ_(ss), θ_(fg) are the angles withrespect to the normal line of the targeted incidence plane. In theincident angle θ_(ss) of the detection light IDL with respect to theprojected screen PS, the incident angle θ_(ss2) obtained in the case inwhich the non-light-emitting pointing element 80 is located in the upperarea is smaller than the incident angle θ_(ss1) obtained in the case inwhich the non-light-emitting pointing element 80 is located in the lowerarea. In contrast, in the incident angle θ_(fg) of the detection lightIDL with respect to the projected screen PS, the incident angle θ_(fg2)obtained in the case in which the non-light-emitting pointing element 80is located in the upper area is larger than the incident angle θ_(fg1)obtained in the case in which the non-light-emitting pointing element 80is located in the lower area. These relationships are expressed as thefollowing formulas.θ_(ss2)<θ_(ss1)  (2a)θ_(fg1)<θ_(fg2)  (2b)

In contrast, the intensity of the reflected light from the projectedscreen PS and the non-light-emitting pointing element 80 can beexpressed as the following formulas.R _(ss) =k _(ss)×cos θ_(ss)  (3a)R _(fg) =k _(fg)×cos θ_(fg)  (3b)

Here, R_(ss) denotes the intensity of the reflected light from theprojected screen PS (i.e., the screen surface SS), k_(ss) denotes thereflectance of the detection light IDL on the screen surface SS, θ_(ss)denotes the incident angle of the detection light IDL with respect tothe projected screen PS. Further, R_(fg) denotes the intensity of thereflected light from the non-light-emitting pointing element 80, k_(fg)denotes the reflectance of the detection light IDL on thenon-light-emitting pointing element 80, θ_(fg) denotes the incidentangle of the detection light IDL with respect to the non-light-emittingpointing element 80. It should be noted that although the intensity ofthe reflected light is inversely proportional to the square of thedistance in reality, since the distances of the both sides can beassumed to be roughly equal to each other, the influence of thedistances is omitted in the formulas (3a), (3b). Since the incidentangles θ_(ss), θ_(fg) have a value in a range of 0 through 90 degrees,the larger the incident angles θ_(ss), θ_(fg) are, the smaller thereflected light intensities R_(ss), R_(fg) becomes.

As is obvious from the formulas (2a), (2b) and the formulas (3a), (3b)described above, as the non-light-emitting pointing element 80 movesupward from the lower area, the incident angle θ_(ss) with respect tothe projected screen PS decreases and the intensity R_(ss) of thereflected light from the projected screen PS increases, and in contrast,the incident angle θ_(fg) with respect to the non-light-emittingpointing element 80 increases and the intensity R_(fg) of the reflectedlight from the non-light-emitting pointing element 80 decreases.Therefore, in the images obtained by imaging the reflected light of thedetection light IDL with the cameras 310, 320, there is a possibilitythat the brightness relationship between the non-light-emitting pointingelement 80 and the projected screen PS as the background of thenon-light-emitting pointing element 80 is reversed between the lowerarea and the upper area in the projected screen PS. Such a tendency asdescribed above is common to both of the two detection light irradiationsections 411, 412.

FIGS. 6A and 6B are explanatory diagrams showing the contrast betweenthe projected screen PS and the non-light-emitting pointing element 80obtained by the detection light respectively emitted from the firstdetection light irradiation section 411 and the second detection lightirradiation section 412 in a comparative manner. FIG. 6A shows adistribution of the contrast of the image obtained by imaging thereflected light with the camera 310 in the case of emitting thedetection light only from the first detection light irradiation section411. In this example, a positive contrast area PA1 exists in a lowerpart of the projected screen PS, a negative contrast area NA1 exists inan upper part of the projected screen PS, and a low contrast area LC1exists in between. Here, the “positive contrast area PA1” denotes thearea where the non-light-emitting pointing element 80 is brighter thanthe projected screen PS, and the contrast becomes higher than athreshold value set in advance. Further, the “negative contrast areaNA1” denotes the area where the non-light-emitting pointing element 80is darker than the projected screen PS, and the contrast becomes higherthan the threshold value set in advance. The “low contrast area LC1”denotes the area where the contrast between the non-light-emittingpointing element 80 and the projected screen PS is equal to or lowerthan the threshold value. It should be noted that the threshold value isa value set in advance for distinguishing the non-light-emittingpointing element 80 from the projected screen PS in the image, and isexperimentally or empirically set in advance in accordance with thedistinguishing method. It should be noted that in either of the positivecontrast area PA1 and the negative contrast area NA1, the contrastbetween the non-light-emitting pointing element 80 and the projectedscreen PS becomes sufficiently high, and therefore, it is possible todistinguish the non-light-emitting pointing element 80 from theprojected screen PS. In contrast, in the low contrast area LC1, sincethe contrast between the non-light-emitting pointing element 80 and theprojected screen PS is low, it is difficult to distinguish thenon-light-emitting pointing element 80 from the projected screen PS.

FIG. 6B shows a distribution of the contrast of the image obtained byimaging the reflected light with the camera 310 in the case of emittingthe detection light only from the second detection light irradiationsection 412. Also in this example, a positive contrast area PA2 existsin a lower part of the projected screen PS, a negative contrast area NA2exists in an upper part of the projected screen PS, and a low contrastarea LC2 exists in between. It should be noted that the three areas NA2,LC2, and PA2 shown in FIG. 6B are located at positions shifted downwardfrom the three areas NA1, LC1, and PA1 shown in FIG. 6A. In other words,in FIG. 6B, the negative contrast area NA2 in the upper part in the areaof the projected screen PS spreads wider compared to the negativecontrast area NA1 shown in FIG. 6A. The reason therefor is that thesecond detection light irradiation section 412 is longer in theperpendicular distance from the projected screen PS than the firstdetection light irradiation section 411, and therefore, the detectionlight IDL from the second detection light irradiation section 412 issmaller in the incident angle θ_(ss) with respect to the projectedscreen PS, and larger in the incident angle θ_(fg) with respect to thenon-light-emitting pointing element 80 compared to the detection lightIDL from the first detection light irradiation section 411.

In FIGS. 6A and 6B, the two detection light irradiation sections 411,412 are disposed so that the low contrast areas LC1, LC2 do not overlapeach other in the area of the projected screen PS. In other words, thearea low in contrast with the detection light from one of the twodetection light irradiation sections 411, 412 is the area (the positivecontrast area or the negative contrast area) equal in contrast to orhigher in contrast than a threshold value with the detection light fromthe other of the two detection light irradiation sections 411, 412.Specifically, the low contrast area LC1 in FIG. 6A is located in thenegative contrast area NA2 in FIG. 6B, and the low contrast area LC2 inFIG. 6B is located in the positive contrast area PA1 in FIG. 6A. As aresult, it is possible to distinguish the non-light-emitting pointingelement 80 from the projected screen PS in the state in which the tip ofthe non-light-emitting pointing element 80 is in contact with anarbitrary position in the projected screen PS. Further, thelight-emitting pointing element 70 can also be distinguished from theprojected screen PS in substantially the same manner. It should be notedthat it is also possible to use the negative contrast areas NA1, NA2instead of using the positive contrast areas PA1, PA2. The boundarylines between the areas shown in FIGS. 6A and 6B can be known by acalibration performed in advance. Further, the positions of therespective areas can previously be registered in a nonvolatile memory(not shown) in the position detection section 600 (FIG. 3) or thecontrol section 700. Alternatively, it is also possible to arrange thatthe projected screen PS is sectioned into two areas, namely an upperarea and a lower area, the non-light-emitting pointing element 80 isidentified using the lower area of the projected screen PS in the caseof emitting the detection light IDL with the first detection lightirradiation section 411, and the non-light-emitting pointing element 80is identified using the upper area of the projected screen PS in thecase of emitting the detection light IDL with the second detection lightirradiation section 412.

It should be noted that the positive contrast area PA1 shown in FIG. 6Aand the negative contrast area NA2 shown in FIG. 6B partially overlapeach other, and in the overlapping area, the positive contrast in FIG.6A is reversed to the negative contrast in FIG. 6B. In such a case, itis preferable for the first detection light irradiation section 411 andthe second detection light irradiation section 412 to emit the detectionlight toward the projected screen at time-multiplexed timings differentfrom each other as shown in FIGS. 6A and 6B. By adopting thisconfiguration, it is possible to distinguish the non-light-emittingpointing element 80 and the light-emitting pointing element 70 from theprojected screen PS in all of the areas of the projected screen PS byusing the images taken at the timings different from each other.

Regarding the images taken by the camera 320, there appear roughly thesame distributions of the contrast areas as shown in FIGS. 6A and 6B. Itshould be noted that since in the present embodiment, the perpendiculardistances of the two cameras 310, 320 from the projected screen PS aredifferent from each other, the distribution of the contrast areas isdifferent between the images respectively taken by the two cameras 310,320. It should be noted that it is preferable for the two detectionlight irradiation sections 411, 412 to be disposed so that the lowcontrast areas LC1, LC2 do not overlap each other also in the imagestaken by the camera 320 similarly to FIGS. 6A and 6B. It should be notedthat it is also possible to dispose the two cameras 310, 320 so that theperpendicular distances of the two cameras 310, 320 from the projectedscreen PS becomes equal to each other.

Incidentally, as shown in FIGS. 5A and 5B, in the present embodiment,the second detection light irradiation section 412 is disposed at theposition having a longer perpendicular distance from the projectedscreen PS than that of the first detection light irradiation section411. In such a case, it is preferable to set the emission intensity ofthe detection light IDL by the second detection light irradiationsection 412 to be higher than the emission intensity of the detectionlight IDL by the first detection light irradiation section 411. Byadopting such a configuration, the contrast in the image taken using thedetection light IDL from the second detection light irradiation section412 can be made sufficiently high.

As described above, in the first embodiment, in the state in which thetip of the pointing element is in contact with the arbitrary position inthe area of the projected screen PS, at least one of the first contrastin the image taken in the case in which the detection light IDL1 isemitted only from the first detection light irradiation section 411, andthe second contrast in the image taken in the case in which thedetection light IDL2 is emitted only from the second detection lightirradiation section 412 becomes higher than the threshold set inadvance. As a result, it is possible to distinguish the pointing element(the non-light-emitting pointing element or the light-emitting pointingelement 70) from the projected screen PS in the arbitrary position inthe area of the projected screen PS.

C. Detection Light Irradiation Section in Second Embodiment

FIG. 7A is a side view of an interactive projection system 900 aaccording to a second embodiment, and FIG. 7B is a front view thereof.The difference from the first embodiment shown in FIGS. 2A and 2B isonly the arrangement of the two detection light irradiation sections411, 412, and the rest is the same as in the first embodiment. The twodetection light irradiation sections 411, 412 are disposed separately onthe right and left sides of the center PSc of the projected screen PS,and emit the respective detection light beams IDL1, IDL2 toward the areaof the projected screen PS. In other words, the two detection lightirradiation sections 411, 412 are disposed on the opposite sides to eachother across a virtual plane including the normal line VNc in the centerPSc of the projected screen PS. Although in FIG. 7B, the detection lightbeams IDL1, IDL2 from the respective two detection light irradiationsections 411, 412 are drawn as if the detection light beams IDL1, IDL2intersect with each other for the sake of convenience of graphicaldescription, in reality, the detection light beams IDL1, IDL2 from thetwo detection light irradiation sections 411, 412 are each emittedtoward the entire area of the projected screen PS.

In the second embodiment, in the case in which the detection light beamIDL1 is emitted only from the first detection light irradiation section411, the three areas NA1, LC1, and PA1 (not shown in FIGS. 7A and 7B)appear on the lower side of the first detection light irradiationsection 411 with substantially the same pattern as shown in FIG. 6A.However, even in the case in which the non-light-emitting pointingelement 80 exists in the negative contrast area NA1 or the low contrastarea LC1, the side surface of the non-light-emitting pointing element 80is irradiated with the detection light beam IDL2 from the seconddetection light irradiation section 412, and therefore, in the imagestaken by the cameras 310, 320, the non-light-emitting pointing element80 becomes brighter than the projected screen PS, and thus the positivecontrast can be obtained. In the case in which the detection light IDL2is emitted only from the second detection light irradiation section 412,in contrast, the positive contrast can be obtained due to the detectionlight beam IDL1 from the first detection light irradiation section 411.Therefore, also in the second embodiment, similarly to the firstembodiment, in the state in which the tip of the pointing element is incontact with the arbitrary position in the area of the projected screenPS, at least one of the first contrast in the image taken in the case inwhich the detection light IDL1 is emitted only from the first detectionlight irradiation section 411, and the second contrast in the imagetaken in the case in which the detection light IDL2 is emitted only fromthe second detection light irradiation section 412 becomes higher thanthe threshold set in advance. As a result, it is possible to distinguishthe pointing element (the non-light-emitting pointing element 80 or thelight-emitting pointing element 70) from the projected screen PS in thearbitrary position in the area of the projected screen PS. It should benoted that in the second embodiment, it is also possible to arrange thatthe two detection light irradiation sections 411, 412 simultaneouslyemit the detection light beams IDL1, IDL2, or arranged that the twodetection light irradiation sections 411, 412 emit the detection lightbeams IDL1, IDL2 in a time-multiplexed manner. It should be noted thatif it is arranged that the two detection light irradiation sections 411,412 emit the detection light beams IDL1, IDL2 at the same time, theoverall processing time can be reduced.

D. Detection Light Irradiation Section in Third Embodiment

FIG. 8A is a side view of an interactive projection system 900 baccording to a third embodiment, and FIG. 8B is a front view thereof.The difference from the second embodiment shown in FIGS. 7A and 7B isonly the point that a third detection light irradiation section 413 isadded in addition to the two detection light irradiation sections 411,412, and the rest is the same as in the second embodiment. The thirddetection light irradiation section 413 is disposed at the positioncloser to the virtual plane including the normal line VNc at the centerPSc of the projected screen PS than the positions of the first detectionlight irradiation section 411 and the second detection light irradiationsection 412, and irradiates throughout the area of the projected screenPS with a detection light beam IDL3.

In the third embodiment, in the case in which the detection light beamIDL3 is emitted only from the third detection light irradiation section413, the three areas NA1, LC1, and PA1 (not shown in FIGS. 8A and 8B)appear similarly to FIG. 6A. However, even in the case in which thenon-light-emitting pointing element 80 exists in the negative contrastarea NA1 or the low contrast area LC1, the side surface of thenon-light-emitting pointing element 80 is irradiated with the detectionlight beam from at least one of the first detection light irradiationsection 411 and the second detection light irradiation section 412, andtherefore, in the images taken by the cameras 310, 320, thenon-light-emitting pointing element 80 becomes brighter than theprojected screen PS, and thus the positive contrast can be obtained.

In the third embodiment, since the higher contrast than in the secondembodiment shown in FIGS. 7A and 7B can be obtained, it is possible todistinguish the non-light-emitting pointing element 80 and thelight-emitting pointing element 70 from the projected screen PS. Itshould be noted that in the third embodiment, it is also possible forthe third detection light irradiation section 413 to irradiate the areaof the projected screen PS simultaneously with the first detection lightirradiation section 411 and the second detection light irradiationsection 412, or to adopt the time-multiplexed method to irradiate thearea of the projected screen PS at timings different from those of thefirst detection light irradiation section 411 or the second detectionlight irradiation section 412.

MODIFIED EXAMPLES

It should be noted that the invention is not limited to the specificexamples and the embodiments described above, but can be put intopractice in various forms within the scope or the spirit of theinvention, and the following modifications, for example, are alsopossible.

Modified Example 1

Although in the embodiments described above, it is assumed that theimaging section 300 includes two cameras 310, 320, the imaging section300 can also include three or more cameras. In the latter case, thethree-dimensional coordinate (X, Y, Z) is determined based on m imagestaken by the m (m is an integer equal to or greater than 3) cameras. Forexample, it is possible to obtain the three-dimensional coordinatesusing _(m)C₂ combinations obtained by arbitrarily selecting two imagesout of the m images, and then obtain the final three-dimensionalcoordinate using the average value of the three-dimensional coordinates.By adopting this configuration, the detection accuracy of thethree-dimensional coordinate can further be improved.

Modified Example 2

Although in the embodiments described above, it is assumed that theinteractive projection system 900 can act in the whiteboard mode and thePC interactive mode, the system can also be configured so as to act ineither one of the modes. Further, it is also possible for theinteractive projection system 900 to be configured so as to act only inother modes than these two modes, or further to be configured so as tobe able to act in a plurality of modes including these two modes.

Modified Example 3

Although in the embodiments described above it is assumed that theirradiating detection light IDL, the reflected detection light RDL, thedevice signal light ASL, and the pointing element signal light PSL shownin FIG. 3 are all the near infrared light, it is also possible to assumethat some or all of these light beams are light other than the nearinfrared light.

Modified Example 4

Although in the embodiments described above, it is assumed that theprojected screen is projected on the screen plate 920 having a flatshape, it is also possible to assume that the projected screen isprojected on a screen having a curved shape. In this case, since thethree-dimensional position of the tip portion of the pointing elementcan also be determined using the triangulation based on the images takenby the two cameras, it is possible to determine the positionalrelationship between the tip portion of the pointing element and theprojected screen.

Although the embodiments of the invention are hereinabove explainedbased on some specific examples, the embodiments of the inventiondescribed above are only for making it easy to understand the invention,but not for limiting the scope of the invention. It is obvious that theinvention can be modified or improved without departing from the scopeof the invention and the appended claims, and that the inventionincludes the equivalents thereof.

What is claimed is:
 1. An interactive projector capable of receiving aninstruction of a user to a projected screen with a pointing element,comprising: a projection section adapted to project the projected screenon a screen surface; a first detection light irradiation section and asecond detection light irradiation section each adapted to emitdetection light used for detection of the pointing element toward anarea of the projected screen such that the emitted detection light fromeach of the first detection light irradiation section and the seconddetection light irradiation section is incident on the area of theprojected screen; an imaging section adapted to receive light in awavelength range including a wavelength of the detection light to takean image of the area of the projected screen; and at least one processoradapted to detect a position of the pointing element with respect to theprojected screen based on an image, which is taken by the imagingsection and includes the pointing element, wherein, in a state in whicha tip of the pointing element is in contact with an arbitrary positionin the area of the projected screen, the first detection lightirradiation section and the second detection light irradiation sectionare disposed so that at least one of the following (i) and (ii) becomeshigher than a threshold value set in advance for distinguishing thepointing element from the projected screen: (i) a first contrast betweenthe pointing element in a first image taken by the imaging section in acase in which the detection light is emitted only from the firstdetection light irradiation section and the area of the projectedscreen, and (ii) a second contrast between the pointing element in asecond image taken by the imaging section in a case in which thedetection light is emitted only from the second detection lightirradiation section and the area of the projected screen, and whereinthe first detection light irradiation section creates a first lowcontrast area on the projected screen and the second detection lightirradiation section creates a second low contrast area on the projectedscreen, the first low contrast area and the second low contrast areacorrespond to areas where contrast between the pointing element and theprojected screen is at or below the threshold value, and the firstdetection light irradiation section and the second detection lightirradiation section are disposed such that the first low contrast areadoes not overlap the second low contrast area on the projected screen.2. The interactive projector according to claim 1, wherein in a state inwhich the tip of the pointing element is in contact with at least a partof the area in the projected screen, the first detection lightirradiation section and the second detection light irradiation sectionare disposed so that if the first contrast is positive, then the secondcontrast is negative, and if the first contrast is negative, then thesecond contrast is positive, and the first detection light irradiationsection and the second detection light irradiation section emit thedetection light toward the projected screen in a time-multiplexedmanner.
 3. The interactive projector according to claim 1, wherein thefirst detection light irradiation section and the second detection lightirradiation section are disposed on opposite sides to each other acrossa virtual plane including a normal line of the projected screen at acenter of the projected screen.
 4. The interactive projector accordingto claim 3, further comprising: a third detection light irradiationsection disposed at a position closer to the virtual plane than thefirst detection light irradiation section and the second detection lightirradiation section, and adapted to irradiate the area of the projectedscreen with the detection light.
 5. An interactive projecting systemcomprising: the projector according to claim 1; and a screen having ascreen surface on which the projected screen is projected.
 6. A methodof controlling an interactive projector capable of receiving aninstruction of a user to a projected screen with a pointing element, themethod comprising: projecting the projected screen on a screen surface;emitting detection light used for detection of the pointing elementtoward an area of the projected screen such that the emitted detectionlight from each of a first detection light irradiation section and asecond detection light irradiation section is incident on the area ofthe projected screen; taking an image of the area of the projectedscreen that includes the pointing element by receiving light in awavelength range including a wavelength of the detection light; anddetecting a position of the pointing element with respect to theprojected screen based on the image of the area of the projected screen,wherein the first detection light irradiation section and the seconddetection light irradiation section are disposed such that, in a statein which a tip of the pointing element is in contact with an arbitraryposition in the area of the projected screen, at least one of thefollowing (i) and (ii) becomes higher than a threshold value set inadvance for distinguishing the pointing element from the projectedscreen: (i) a first contrast between the pointing element in a firstimage taken of the area of the projected screen in a case in which thedetection light is emitted only from the first detection lightirradiation section and the area of the projected screen, and (ii) asecond contrast between the pointing element in a second image taken ofthe area of the projected screen in a case in which the detection lightis emitted only from the second detection light irradiation section andthe area of the projected screen, the first detection light irradiationsection creates a first low contrast area on the projected screen andthe second detection light irradiation section creates a second lowcontrast area on the projected screen, the first low contrast area andthe second low contrast area correspond to areas where contrast betweenthe pointing element and the projected screen is at or below thethreshold value, and the first detection light irradiation section andthe second detection light irradiation section are disposed such thatthe first low contrast area does not overlap the second low contrastarea on the projected screen.
 7. The method according to claim 6,wherein in a state in which the tip of the pointing element is incontact with at least a part of the area in the projected screen, thefirst detection light irradiation section and the second detection lightirradiation section are disposed so that if the first contrast ispositive, then the second contrast is negative, and if the firstcontrast is negative, then the second contrast is positive, and theemitting of the detection light includes emitting the detection lighttoward the projected screen in a time-multiplexed manner.
 8. The methodaccording to claim 6, wherein the first detection light irradiationsection and the second detection light irradiation section arepositioned such that they are disposed on opposite sides to each otheracross a virtual plane including a normal line of the projected screenat a center of the projected screen.
 9. The method according to claim 8,wherein the emitting of the detection light further comprises emittingthe detection light from a third detection light irradiation sectiondisposed at a position closer to the virtual plane than the firstdetection light irradiation section and the second detection lightirradiation section.